I think using !important is not a very wise option. It may cause for many other issues specially when making the site responsive. So, my understanding is that, the best way to do this to use custom button CSS class with .btn bootstrap class. .btn is the base style class for bootstrap button. So, keep that as the layout, we can change other styles using our custom css class.
我还有一件事要说。有些人正试图从按钮上去除蓝色的轮廓。这不是一个好主意,因为在使用键盘时存在可访问性问题。改变它的颜色使用 outline-color:代替。